1. Filed of the Invention
The present invention relates to an AC memory type plasma display panel. More specifically it relates to a plasma display panel for stably generating a writing discharge.
2. Description of the Related Art
A plasma display panel generally contains the following characteristics. A plasma display panel has a thin structure. It hardly generates flickers. It provides a high display contrast. It may have a relatively large screen. It provides a high response speed. It is a self-light-emitting type, and may provide multiple color light emission by means of the phosphor. The uses of plasma display panels have been increasing in the fields of large public display apparatuses and color television sets and the like recently.
The operation type of plasma display panel is classified into two categories: AC discharge type (AC type), which has electrodes covered by a dielectric material, and operates in an indirect AC discharge state; and DC discharge type (DC type), which has electrodes exposed to a discharge space, and operates in a DC discharge state. The AC discharge type is further classified into memory operation type, which uses a memory of a discharge cell, and refresh operation type, which does not use a discharge cell. The luminance of a plasma display panel is approximately proportional to the number of discharges, namely, the number of repetitions of a pulse, whether it is the memory operation type or the refresh operation type. Because the refresh type presents a decrease in luminosity as display capacity increases, it is mainly used for small display capacity applications.
FIG. 1 is an exploded oblique perspective view of a display cell constitution in a standard AC discharge memory operation type plasma display panel.
The plasma display panel is provided with front and rear insulation substrates 1 and 2 made of glass. A transparent scanning electrode 3 and a transparent sustaining electrode 4 are formed on the insulation substrate 2 and are placed in parallel with each other. Bus electrodes 5 and 6 are placed so as to overlap the scanning electrode 3 and the sustaining electrode 4 for reducing electrode resistances. Data electrodes 7 crossing the scanning electrode 3 and the sustaining electrode 4 are formed on the insulation substrate 1. A discharge gas space 8 is formed between the insulation substrates 1 and 2 where discharge gas containing helium, neon, xenon or the like, or mixed gas thereof is filled. Phosphor layers 9 are formed to convert ultraviolet ray generated by a discharge of the discharge gas into visible light 14. A dielectric material layer 10 covering the scanning electrode 3 and the sustaining electrode 4 are formed on the insulation substrate 1. A protection layer 11 made of magnesium oxide or the like and protecting the dielectric material layer 10 from the discharge is formed on the dielectric material layer 10. A dielectric material layer 12 covering the data electrode 7 is formed on the insulation substrate 2. Partition walls 13 separating neighboring display cells are formed on the dielectric material layer 12. The surface of data electrode 7 is covered with the dielectric layer 12. The partition wall 13 for separating the display cells is provided between the neighboring data electrodes 7 on the dielectric layer 12. The phosphor layer 9 is applied to the dielectric material layer 12 between the partition walls 13, and on the side faces of partition walls 13. The phosphor layer 9 is painted in three primary colors including red, green and blue, and is arranged to display different colors.
FIG. 2 is a vertical section view showing the display cell in the AC discharge memory operation type plasma display panel shown in FIG. 1.
The following section describes a discharge operation of a selected display cell while referring to FIG. 2.
When a pulse voltage exceeding a discharge threshold is applied between the scanning electrode 3 and the data electrode 7 of individual display cells to start a discharge, negative and positive electric charges are attracted on the surfaces of dielectric material layers 10 and 12 according to the polarity of pulse voltage, thereby generating electric charge accumulations. An equivalent internal voltage caused by these electric charge accumulations, namely, a wall voltage, has a polarity reverse to the pulse voltage. Thus, because an effective voltage in the cell decreases as the discharge grows, maintaining the pulse voltage to a constant value does not keep the discharge, and the discharge finally stops.
When a discharge starts between the scanning electrode 3 and the data electrode 7, this discharge triggers a discharge between the scanning electrode 3 and the sustaining electrode 4 if a voltage more than a certain level is applied between the scanning electrode 3 and the sustaining electrode 4. As the result, electric charge accumulations are generated in the dielectric layer 10 so as to cancel the voltage applied at this moment as the discharge between the scanning electrode 3 and the data electrode 7.
Then, a sustaining discharge pulse, which has a pulse voltage with a polarity same as the wall voltage, is applied between the scanning electrode 3 and the sustaining electrode 4, a voltage corresponding to the wall voltage is superimposed as an effective voltage, and the discharge occurs exceeding the discharge threshold when a voltage amplitude of the sustaining discharge pulse is low. Thus, keeping the sustaining discharge pulse applied alternately between the scanning electrode 3 and the sustaining electrode 4 maintains the discharge. This function is the memory function described before.
FIG. 3 is a block diagram showing a constitution of a display apparatus using a plasma display panel where the display cells shown in FIG. 2 are formed as a matrix arrangement.
A plasma display panel 15 is a panel for dot matrix display where the display cells 16 are arranged as mxc3x97n of rows and columns. As row electrodes, scanning electrodes X1, X2, . . . , Xm and sustaining electrodes Y1, Y2, . . . , Ym are provided in parallel with one another. As column electrodes, data electrodes D1, D2, . . . , Dn are arranged in crossing the scanning electrodes and the sustaining electrodes.
A scanning driver 17 applies a scanning electrode drive wave on the scanning electrodes X1, X2, . . . , Xm. A sustaining driver 18 applies a sustaining electrode drive wave on the sustaining electrodes Y1, Y2, . . . , Ym. A data driver 19 applies a data electrode drive wave on the data electrodes D1, D2, . . . , Dn.
A control circuit 20 generates control signals for the individual drivers based on base signals (Vsync, Hsync, Clock, and DATA). The control circuit 20 is provided with a signal processing and memory controller 20a for generating control signals for a frame memory and a driver-controller from the base signals, a frame memory 20b for storing the DATA signal, which is image data, and a driver-controller 20c for generating the control signals for the individual electrode drivers.
FIG. 4 is a timing chart showing driving signal waveforms provided from the scanning driver 17, the sustaining driver 18, and the data driver 19.
Wu indicates a sustaining electrode driving pulse applied commonly on the sustaining electrodes Y, Y2, . . . , Ym, Ws1, Ws2, . . . , Ws3 indicate scanning electrode driving pulses applied respectively on the scanning electrodes X1, X2, . . . , Xm, and Wd indicates a data electrode driving pulse applied on a data electrode Di (1xe2x89xa6ixe2x89xa6n) in FIG. 4.
One cycle of the driving (1 Sub-Field: SF) is composed of a preliminary discharge period, a writing discharge period, a sustaining discharge period, and an erasing discharge period, and repeating them provides a desired video image display.
The preliminary discharge period is a period for generating active particles in the discharge gas space 8, and wall electric charges to obtain a stable writing discharge characteristic in the writing discharge period. After a pre-discharge pulse Pp is applied for simultaneously discharging all display cells on the plasma display panel 15, a preliminary discharge erasing pulse Ppe is simultaneously applied on the individual scanning electrodes for removing electric charge that inhibits the writing discharge and the sustaining discharge from the generated wall electric charges, in the preliminary discharge period. Namely, after the preliminary discharge pulse Pp is applied on the scanning electrodes X1, X2, . . . , Xm to start the discharge all the display cells, the sustaining electrodes Y1, Y2, . . . , Ym are brought up to a sustaining voltage level Vs. Then, the preliminary discharge erasing pulse Ppe is applied on the scanning electrodes X1, X2, . . . , Xm to generate an erasing discharge, thereby gradually decrease their voltages, resulting in erasing the wall electric charges accumulated by the preliminary discharge pulse. The erasing here includes adjusting the amount of wall electric charges for smoothly conducting the following writing discharge and sustaining discharge in addition to removing the wall electric charge entirely.
A scanning pulse Pw is sequentially applied on the individual scanning electrodes X1, X2, . . . , Xm, and a data pulse Pd is selectively applied on the data electrodes Di (1xe2x89xa6ixe2x89xa6n) in the display cells that display in synchronous with the scanning pulse Pw in the writing discharge period. As the result, the writing discharge is generated in the cells that display to generate wall electric charge.
A sustaining discharge pulse Pc is applied on the sustaining electrodes, and a sustaining discharge pulse Ps whose phase is delayed by 180 degree than the sustaining discharge pulse Pc is applied on the individual scanning electrodes in the sustaining discharge period. Necessary sustaining discharge is repeated to obtain required luminance on the display cells where the writing discharges are conducted during the writing discharge period.
Finally, an erasing pulse Pe is applied on the scanning electrodes X1, X2, . . . , Xm to gradually decrease their voltages, thereby generating an erasing discharge, resulting in removing the wall electric charges accumulated by the sustaining discharge pulses in the erasing discharge period. The erasing here includes adjusting the amount of wall electric charge for smoothly conducting the following preliminary discharge, writing discharge and sustaining discharge in addition to removing the wall electric charges entirely.
It is desirable that a matrix discharge tends to start between the scanning electrode and the data electrode during the writing discharge, and this matrix discharge quickly triggers a surface discharge between the scanning electrode and the sustaining electrode in this driving method. This is because that conducting these discharges stably means displaying an input image precisely.
Publication of unexamined patent application No. Hei 10-302643 discloses a method for decreasing the width of a scanning electrode than that of a sustaining electrode for stabilizing the writing discharge.
FIG. 5 is a vertical section view showing a structure of a display cell disclosed in publication of unexamined patent application H10-302643. This prior art decreases the width of scanning electrode 3 in the standard display cell structure shown in FIG. 1, namely, the length of electrode in the horizontal direction than that of the sustaining electrode 4 in FIG. 5. In this case, because the area where the scanning electrode 3 faces the data electrode 7 decreases, the transition to the surface discharge tends to occur.
An extension of the sustaining discharge in the individual display cells on the AC type plasma display panel depends on an area where the scanning electrode and the sustaining electrode are formed, and the sustaining discharge area becomes wider as this area becomes wider. As the sustaining discharge area increases, the amount and the area of ultraviolet ray increase in the display cell, thereby increasing stimulating quantity to the phosphor, resulting in increasing the luminance.
This means that as the screen size of a plasma display panel increases, and the size of individual display cells increases, the electrode area naturally increases, thereby providing a bright image. On the other hand, the matrix discharge area during the writing discharge increases, the transition characteristic to the surface discharge decreases, thereby preventing a stable image display.
FIG. 6 is a schematic view showing a state of the writing discharge of the plasma display panel shown in FIG. 2. Here, only the matrix discharge is shown, and the surface discharge that triggered it is suppressed.
As shown in FIG. 6, when the area of scanning electrode 3 is large, and an overlap with the data electrode 7 is large, an area where a matrix discharge starts varies. In this state, though if a matrix discharge is generated in an area close to the sustaining electrode 4, it easily changes to a surface discharge, if a matrix discharge is generated in an area far from the sustaining electrode 4, it hardly changes to a surface discharge. It is required to applying a higher voltage between the data electrode 7 and the scanning electrode 3 to strengthen the matrix discharge, and to increasing the voltage applied between the sustaining electrode 4 and the scanning electrode 3 during the writing discharge, in order to properly generate the surface discharge in any states of the matrix discharge.
When the applied voltage increases, a driver with a higher withstand voltage is required, and the power consumption increases. Also, the extensions of individual matrix discharge areas become relatively wide, thereby increasing matrix discharge current, resulting in requiring application of the scanning driver and the data driver with higher output current capability.
On the other hand, because the conventional plasma display panel shown in FIG. 5 has the scanning electrode 3 with the narrower width, though the variation of area where the matrix discharge occurs decreases, and the transition characteristic from the matrix discharge to the surface discharge becomes smooth, the extension of sustaining discharge becomes smaller.
FIGS. 7A and 7B are schematic views showing a state of a sustaining discharge of the plasma display panel shown in FIG. 5. FIG. 7A shows a discharge state where the sustaining electrode 4 is set to an electric potential of 0 V, and the scanning electrode 3 is set to an electric potential of Vs, and FIG. 7B shows a discharge state where the sustaining electrode 4 is set to an electric potential of Vs, and the scanning electrode 3 is set to an electric potential of 0 V. The respective wall electric charges are those accumulated after the sustaining discharge occurs.
The extension of a sustaining discharge follows areas where the sustaining electrode 4 and the scanning electrode 3 are provided, and reaches to mutually further ends of the sustaining electrode 4 and the scanning electrode as shown in FIG. 7A and FIG. 7B. Because ultraviolet ray generated by this discharge is projected isotropically, it stimulates areas of the phosphor that do not oppose to the electrode, and is converted into visible light. Namely, the visible light is observed on the outside of scanning electrode (further side from the sustaining electrode). The amount of ultraviolet ray reaching to these areas is smaller than that in the area where the scanning electrode exists because the distance between the discharging area and the phosphor is large, thereby decreasing the converted amount to the visible light, resulting in emitting dark light.
It is an object of the present invention is to provide a plasma display panel with high luminance while stabilizing a writing discharge.
A plasma display panel according to the present invention comprises a transparent substrate, and scanning electrodes and sustaining electrodes formed on the transparent substrate, constituting surface discharge electrodes, and extending in a first direction. An area of the scanning electrode is smaller than an area of the sustaining electrode in each of display cells. The widths of the scanning electrode and the sustaining electrode in a second direction crossing the first direction are substantially equal to each other.
According to the present invention, it is possible to reduce an matrix discharge current during a writing discharge, to increase a transition characteristic from an matrix discharge to a surface discharge, and to increase the luminance. If the scanning electrode and the sustaining electrode are isolated in the display cells, it is possible to increase luminous efficiency, and to reduce charging/discharging power as well.